Many miles of existing highways utilize asphalt-containing materials in combination with various aggregates such as gravel, crushed stone, and sand. In addition, numerous additional miles of roads are built each year, in which asphalt serves as one of the major components. The continued widespread use of such material, however, depends susbstantially upon cost, durability of the paved surface, the frequency and the nature of required maintenance in response to weather and vehicular-induced damage.
Generally speaking, when repair or resurfacing is carried out, hot asphalt or asphalt emulsion are applied in one form or another to fill road cracks and joints, as waterproof underlayers between old and new paving surfaces, and as the external surfacing material. For each purpose, however, the amount and fineness of aggregate, the nature and amount of curing and thickening agents and the presence and concentration of other additives can vary widely, depending on the geographic location, traffic density, and required ease of application under ambient conditions.
By way of example, asphalt paving compositions exhibiting flexibility, strength and toughness can be obtained even under zero conditions by including, within the composition, about 1%-10% by weight of organic staple fiber such as a polyolefin or polyester. Addition of such reinforcing fiber to asphalt, however, can also have a negative effect since it dramatically reduces pumpability and workability of the resulting composition. In normal usage, for example, hot asphalt concrete mixes are generally heated to about 230.degree. F. to 245.degree. F. before lay-down. Upon addition of reinforcing fiber, however, the composition temperature must be raised at least about 10.degree. higher to obtain acceptable lay-down and compaction characteristics. This additional heating is generally undesirable due to energy cost factors and possible heat-induced fiber degredation.
It has also been found that the above pumpability and workability problems can be minimized by also including about 0.5%-10% by weight of a straight chain unsaturated fatty acid containing up to about 30 weight % rosin, such as tall oil fatty acids..sup.(*) Such advantage is paid for, however, by substantially lowered resistance to tracking and increased washing effect under hot summer conditions. FNT * Commercially available from Hercules Incorporated as Pamak.RTM. tall oil fatty acids. See also Hackh's Chemical Dictionary 4th Ed. pg. 660 and Condensed Chemical Dictionary, 10th Ed. pg. 992.
This latter problem can be controlled to some extent by the increased use of fine aggregate (i.e., sand) and filler (i.e., talc). Such materials however are not easily uniformly dispersed or kept in such condition within the body of an asphalt paving or sealing composition. Sand, for instance, begins to settle and irregular particles tend to block applicator passages.
It is an object of the present invention to help control the tracking and washing characteristics of fiber-reinforced asphalt paving and sealing compositions containing unsaturated fatty acids and rosin additives.
It is a further object of the present invention to avoid the use of excessive amounts of inorganic aggregate and filler, particularly fine aggregate, to promote stability of tall oil fatty acid-containing fiber reinforced asphalt-based paving and sealing compositions under a combination of summer heat and vehicular pounding.